1. Field of the Invention
The invention is related to the field of removing noise from a flow meter signal, and in particular, to removing cyclic noise, such as cross-talk noise, from the flow meter signal.
2. Statement of the Problem
Flow meters are used to measure the mass flow rate, density, and other information for flowing materials. The flowing materials can include liquids, gases, combined liquids and gases, solids suspended in liquids, and liquids including gases and suspended solids. For example, flow meters are widely used in the well production and refining of petroleum and petroleum products. A flow meter can be used to determine well production by measuring a flow rate (i.e., by measuring a mass flow through the flow meter), and can even be used to determine the relative proportions of the gas and liquid components of a flow.
In a production or processing environment, it is common to have multiple flow meters connected to the same process line and/or mounted in such a manner that vibration from one flow meter can reach another flow meter. Although this results in efficiency in measuring flow, the multiple flow meters can interfere with each other in the form of cross-talk noise. Cross-talk is a phenomena when the flow meter signal from a first meter influences and corrupts a flow meter signal from a second flow meter (and vice versa). Cross-talk noise in a flow meter environment commonly is a relatively large, slow-moving signal typically no faster than 1 Hertz (Hz). The noise can degrade accuracy of the flowmeter signal and can lead to extremely large indicated flow errors. In addition, noise can occur due to other factors and other sources.
FIG. 1 is a graph of a flow meter output signal taken over time. The figure shows how a flow meter signal is influenced by other flow meters. The time periods 101 and 103 in the figure show a flow meter signal when three flow meters are generating output, with two other flow meters therefore generating cross-talk noise in the current flow meter output. Time period 102 is a flow meter signal when only one other interfering flow meter is active. Note that the generated noise varies in both amplitude and frequency throughout the graph.
The prior art has attempted to address noise and cross-talk noise through use of traditional filtering techniques, such as high-pass filtering. However, due to the relatively small difference in frequencies between cross-talk noise and the actual flow meter data, and due to the low frequency data signals outputted by flow meters, it has been difficult to remove noise without degrading the flow meter data.